The present invention relates to an optical communication device for data communication by transmitting a laser beam, which is modulated in accordance with data to be transmitted, through an optical fiber.
An optical communication device generally includes a laser diode and a converging lens. The laser diode emits a laser beam which is modulated in accordance with data to be transferred. The modulated laser beam is converged by the converging lens on an entrance face of an optical fiber that is connected to the optical communication device. In particular, in the optical communication device known as an ONU (Optical Network Unit), a single optical fiber is used for two-way communication. For this purpose, a light receiving element and a WDM (Wavelength Division Multiplex) filter for separating light having different wavelengths are provided.
In order to efficiently transmit the laser beam through the optical fiber in such an optical communication device, the laser beam should be converged on the center of the core of the entrance face of the optical fiber. This requires very precise positioning of the laser diode and the converging lens against the optical fiber.
An example of a conventional method for positioning the laser diode and the converging lens against the optical fiber is disclosed in Japanese Patent Provisional Publication No. HEI 6-94947. According to the method disclosed in the publication, the light amount of the laser beam passed through the optical fiber is detected at an emerging end. The optical fiber is moved relative to the laser beam until the detected light amount exceeds a predetermined threshold value. When the detected light amount exceeds the predetermined threshold value (preferably, the light amount becomes its maximum value), it is determined that the laser beam emitted from the laser diode impinges on the center of the core of the optical fiber.
However, since it is difficult to visually distinguish the core of the entrance face of the optical fiber from the cladding, the position of the laser diode relative to the optical fiber must be first adjusted by trial and error until the laser beam enters the core of the optical fiber and can be detected on the other end of the optical fiber. This process is troublesome and time consuming.
When the positioning of the laser diode and the converging lens with respect to the optical fiber is achieved, the laser diode and the converging lens are fixed in the optical communication device by an adhesive, for example. However, since the adhesive contracts during a hardening process thereof, the proper alignment of the laser diode, the converging lens, and the optical fiber may be lost due to the contraction of the adhesive, which may worsen the positional relationship of the laser diode and/or the converging lens with respect to the optical fiber. Further, there is also a possibility that the positional relationship of the laser diode and/or the converging lens with respect to the optical fiber may change with time.
In the conventional optical communication device, however, once the laser diode and the converging lens are fixed to the device, it is impossible to re-adjust the positions thereof.